The present invention relates to N-substituted carbamates, and particularly to a catalyst for preparing these N-substituted carbamates. This invention also relates to the novel catalyst, to the preparation of the catalyst, and to the use thereof.
N-substituted carbamates represent a class of important organic intermediates, which can be used for the manufacture of agrochemicals, dyes, pharmaceuticals, ureas, and isocyanates. Furthermore, they can also be applied as protective groups of amides in various organic syntheses.
The synthesis of N-substituted carbamates has received considerable attention due to their wide applications. For example, U.S. Pat. No. 3,763,217 and U.S. Pat. No. 4,268,683 disclose the synthesis of N-substituted carbamates by reacting aromatic amines with organic carbonates in the presence of AlCl3, FeCl3, UO2(NO)2, zinc acetate, zinc propionate, or zinc naphthenate as a catalyst, respectively. This method has low selectivity for the desired products. Moreover, the catalyst activity is restricted by the aromatic amines. Both DE 2943480 and U.S. Pat. No. 4,381,403 disclose that homogeneous ZnCl2 or tertiary amine can be used as a catalyst in the synthesis of N-substituted carbamates by reacting carbamates and amines. However, these catalysts are difficult to separate and recover from the reaction mixtures. Thus, these catalyst can not be conveniently recycled.
From the perspective of commercial application, it is necessary to develop a new catalyst for preparing N-substituted carbamates. The catalyst should not only be capable of preparing the targeted products in high yields, but should also be convenient to separate from the product and recycled.